Carbamyl phosphate is a key intermediate in the biosynthesis of pyrimidines and of arginine and is therefore an essential molecule for the synthesis of both nucleic acids and proteins. Carbamyl phosphate synthetases are found in bacteria, animal tissues and plants and are subject to allosteric regulation by a number of purine and pyrimidine nucleotides and by ornithine. The objectives of this proposal are twofold: 1) to obtain data on the mechanism of action of carbamyl phosphate synthetases by steady-state and rapid-flow kinetic techniques and by isotopic scrambling methods, and 2) to obtain structural data on the topography of substrate and allosteric effector molecule binding sites by nmr, epr and fluorescence energy transfer techniques. Overall both objectives will yield unique information on the regulation of the biosynthesis of an essential metabolite, carbamyl phosphate. These studies will provide structure-function relationships on the basic question of allosteric control of enzymatic catalysis.